The present invention relates to systems for determining distances on golf courses, and more particularly to systems that determine golf course distances using Global Positioning System navigation signals.
The popularity of the game of golf has increased significantly over the past few decades, and the sport is now a major leisure time activity. Hitting a good golf shot (and thus achieving a good golf score) requires that the golfer know with some accuracy the distance the golfer needs to hit the golf ball. Off the tee, for example, the distance required in order to clear a fairway bunker or a water hazard is often a concern. When approaching the green, the distance to the pin or the distance to the front or back of the green must be known in order to enable proper club selection. In summary, then, golfers need to know where their ball lies relative to various points of interest on the golf course, including the pin, the front or back of the green, sand traps, trees, creeks, lakes, and other points of interest.
Various methods for determining the distance to golf course points of interest have been developed. These methods include techniques as simple as walking off the distance between the ball and the point of interest, referring to rough distance markers along the fairway (such as sprinkler heads or 150-yard-markers) and guessing based on vision. While these simple techniques have served golfers for centuries, other more technologically advanced systems have more recently been devised. More advanced systems include the use of binoculars with built-in laser range-finding devices and the use of electronic point identifier units. With the binocular-laser systems, the binoculars include a distance unit that enables a golfer to locate an object. When activated, the distance unit on the binoculars sends a laser signal to the object and the distance between the golfer and the object can be determined by evaluating the laser reflection. With the point identifier units, a stationary electronic unit may be placed on a point of interest, such as a flag pole, and when the golfer directs a point identifier unit towards the pin, the unit transmits a signal to the stationary electronic unit and determines the distance between the point identifier unit and the golfer unit. While each of these systems can be used to determine the distance to a golf pin or other point of interest, these systems have disadvantages. To overcome some of these disadvantages, range finders based on Global Positioning System (xe2x80x9cGPSxe2x80x9d) receivers have been developed.
The United States Department of Defense developed and maintains a constellation of earth-orbiting satellites known as the Global Positioning System to provide radionavigation aids to commercial and military users. The satellite constellation consists of 24 satellites configured in six orbital planes. Radio transmissions from the satellites are referenced to very accurate atomic frequency standards aboard the satellites, which are, in turn synchronized with a system-wide GPS system time base. The system provides accurate, continuous, worldwide, three-dimensional position and velocity information to users with appropriate receiving equipment. A number of standard GPS receivers have been developed for use in aircraft, boats, automobiles and other vehicles, and positioning receivers that use the GPS system have been widely deployed around the world.
The GPS satellites broadcast a pseudo-random-noise code (xe2x80x9cPRN codexe2x80x9d) and navigation data modulated on two carrier frequencies via a spread-spectrum technique called Code Division Multiple Access (xe2x80x9cCDMAxe2x80x9d). All satellites transmit signals with the same two frequencies, but each satellite uses a PRN code that is relatively orthogonal, and hence uncorrelated, with respect to the CDMA codes used by other satellites in the constellation. Navigation data transmitted by each satellite allows receivers to determine the location of the transmitting satellite at the time of transmission, while the PRN code allows receivers to determine which satellite transmitted the signal. The transit time of each signal, and hence the satellite-to-receiver range and the position of the receiver, can be determined once the signals from multiple satellites have been distinguished.
GPS provides service enabling positioning accuracy of about 100 meters to any user worldwide. However, U.S military users can access the GPS xe2x80x9cprecisionxe2x80x9d service that provides considerably more accuracy if they have keys to an encrypted dithering of the satellite clock. In addition, all users can use xe2x80x9cdifferentialxe2x80x9d techniques to obtain far greater position accuracy, such as by removing correlated errors between two or more receivers when the location of one receiver is very precisely known beforehand.
The most common method of calculating position using the GPS satellites is to measure the receiver""s distance (or xe2x80x9crangexe2x80x9d) from at least four GPS satellites in known locations, and to triangulate the receiver""s position therefrom. The range from the receiver to each satellite is measured indirectly by measuring the time for the radio signal transmitted by each satellite to travel through space to the receiver.
This time measurement is made through the use of the PRN code generated by each satellite and transmitted at a precisely determined interval of GPS time that is common to all the satellites Standard GPS receivers are equipped to generate internally an exact duplicate of the unique code transmitted by each satellite. The receiver xe2x80x9ctracksxe2x80x9d or xe2x80x9clocks onxe2x80x9dto a particular satellite by matching or correlating the internally generated code assigned to a particular satellite to the code received as part of the signal transmitted by that satellite. Since some amount of time is required for the coded signal to travel at the speed of light from the satellite to the receiver, the receiver must delay the generation of the internally generated code in order to match the internally generated code to, the code being received. By measuring the amount of time by which the internally generated code must be delayed in order to match the coded signal received from the satellite, the receiver is indirectly measuring the time required for the signal to travel from the satellite to the receiver. Multiplying the time required to travel from the satellite to the receiver by the speed at which the radio signal is traveling (the speed of light), the user can determine the xe2x80x9crangexe2x80x9d or distance to the satellite.
A GPS receiver at a known (i.e., surveyed) location can be used to provide correlated error corrections which can then be transmitted to other nearby receivers to enable more accurate position determination. These receivers use these error corrections in combination with their GPS-derived apparent position data to produce a more accurate differential GPS (DGPS) position correction. DGPS techniques are frequently implemented to achieve a higher degree of accuracy than possible with absolute (single receiver) measurements. When both the base station units and mobile units are within a few miles of each other, DGPS can remove common-mode errors that affect absolute single receiver measurements. These common-mode errors include selective availability (SA) and bias errors, such as satellite clock errors, ephemeris data errors and tropospheric delay effects. DGPS does not correct errors due to multi-path or noise detected at the receiver.
In a typical DGPS-based golf range-finding system, the location of a golfer or mobile unit associated with the golfer may be determined using a standard GPS receiver. Many of these range-finding systems include a fixed, central base station at the golf course clubhouse and numerous mobile units that are either mounted on golf carts or carried by the golfer. Mobile units typically include both a GPS receiver for position determination and a radio communications transceiver for communicating with the central base station. The mobile units typically store a database of records that include the locations of various points of interest on the golf course. The base station unit calculates its GPS position from the signals and compares the calculated position signal to the known fixed location of the base station to compute a differential position correction. These differential position corrections are transmitted to the mobile units to enable the mobile units to correct for correlated positioning errors and to thereby determine a more accurate position estimate than would otherwise be possible with an uncorrected GPS position reading.
While using GPS- and DGPS-based golf ranging systems to provide position estimates to conventional mobile distance units operated by golfers is useful, pin changes and the associated updates must be completed before the golfer begins the round so that the mobile unit can be updated with the correct positions. Because the pin positions on a golf course are routinely changed in the morning after some golfers begin to play, the mobile units operated by the golfers may not have the most recent pin positions information. In other GPS mobile distance systems for golf courses, the pin positions are determined by basing distance calculations on a pre-determined daily pin area position. With the day of week identified, the distance to the pin position area for the day of the week can be determined. However, these estimates may not be as accurate as a golfer would like. Furthermore, although DGPS systems are accurate, some golfers, particularly expert golfers, prefer that the system yield a better margin of error than these systems typically provide.
In order to provide a more accurate GPS-based position determining system for critical aircraft traffic control and automated landing systems, the U.S. Federal Aviation Administration is developing the Wide Area Augmentation System (WAAS). The WAAS improves the accuracy capability of a GPS-based positioning system in much the same way that a ground-based DGPS system does. WAAS is based on a network of approximately 25 ground reference stations that covers a very large service area in North America Signals from GPS satellites are received by wide area ground reference stations (WRSs). Each of these precisely surveyed reference stations receives GPS signals and determines a correction signal required to correct for errors in the GPS-derived position at that point These WRSs are linked to form the U.S. WAAS network. Each WRS in the network relays the data to the wide area master station (WMS) where correction information is computed. The WMS calculates correction algorithms and assesses the integrity of the system. A correction message is prepared and uplinked to a geostationary communications satellite The WAAS correction message is then broadcast by the geostationary satellite at the same frequency that the GPS satellites transmit the GPS navigation code. (1575.42 MHz) to WAAS-equipped receivers onboard aircraft or on the ground that are within the broadcast coverage area of the WAAS. Because the WAAS signal is broadcast at the GPS navigation signal frequency, standard GPS receivers can be easily modified to receive and decode the WAAS correction message and to thereby enable more accurate position determination than is possible using GPS alone. It is expected that in the near future many GPS receivers will be equipped with built-in WAAS capability.
Conventional GPS-based golf range-finding systems suffer from a number of practical limitations, unfortunately. Golf courses increasingly require that golfers refrain from driving their golf carts into the fairway and that the carts instead remain on the asphalt or concrete xe2x80x9ccart pathsxe2x80x9d that extend from tee to green on one side of a typical golf hole. Such xe2x80x9ccart path onlyxe2x80x9d rules help maintain the quality of the turf in the fairway, particularly after a rain when the ground is soft. GPS-based range-finding systems that are mounted in the cart are thus of little use if the cart cannot be driven to the golfer""s ball. Portable GPS-based range-finders that can be carried by the golfer to the ball have been developed to solve the xe2x80x9ccart path onlyxe2x80x9d problem and to service golfers who walk the course rather than ride in a cart. In order to take advantage of real-time DGPS or WAAS position correction systems, communications links to a central base station, and the availability of large display screens for displaying course detail and other rich information, however, these portable units typically must include an RF transceiver, significant battery storage, and a large display screen in addition to a GPS receiver and distance determination capability and are thus large, heavy and more expensive.
Unfortunately, conventional GPS-based golf range-finding systems thus require a performance and cost trade-off. If the system is cart-mounted, full features, a large display screen, and rich functionality can be provided, but the system is not useful in xe2x80x9ccart path onlyxe2x80x9dsituations or when the golfer otherwise leaves the golf cart. If, on the other hand, a portable unit is desired, features and functionality must conventionally be sacrificed in order to minimize size, weight, power consumption, and cost.
A GPS-based position determining system for use on a golf course is provided that combines the benefits of the full features, large display screen, and rich functionality that are available with a cart-mounted GPS-based system and the benefits of the portability, small size, low power consumption, and low cost of a hand-held unit. The hand-held unit can be interconnected with a cart-based unit when it is inserted into a connector cradle in the cart-based unit, and the two units can thereby exchange GPS correction signals, WAAS correction data, location and distance information, paging information, and other information. The performance and cost trade-offs by which conventional systems for GPS-based golf course position determination are constrained are thus avoided.
According to one embodiment, the invention provides a system for receiving position data from GPS satellites and for determining distances to a plurality of selected points of interest on a golf course. The system includes a central base station unit that comprises a base station RF transceiver adapted to communicate via a wireless communications link and a base station controller adapted to control the base station RF transceiver. The system further includes a hand-held unit that comprises a hand-held unit GPS receiver adapted to receive and process navigation signals from GPS satellites and to thereby provide GPS-derived hand-held unit location data, a hand-held unit display for displaying graphics, distance information, location information, and other information to users of the system, a hand-held unit memory for storing a plurality of stored location data, and a hand-held unit controller adapted to control the hand-held unit GPS receiver, the hand-held unit display, and the hand-held unit memory. According to the invention, the hand-held unit is still further adapted to calculate a distance between the hand-held unit and a point of interest on the golf course by comparing the hand-held unit location information with the stored location data for the selected point of interest. The system still further includes a cart-based unit that comprises a cart-based unit battery, a cart-based unit RF transceiver to communicate with the base station RF transceiver via the wireless communications link, and a cart-based unit display for displaying graphics, distance information, location information, and other information to users of the system. The cart-based unit further comprises a connector cradle for holding the hand-held unit. The connector cradle includes a battery connector adapted to electrically connect the cart-based unit battery to the connector cradle, a hand-held unit connector adapted to electrically interconnect the cart-based unit and the hand-held unit when the hand-held unit is received in the connector cradle, and a DC power connector for providing energy from the cart-based unit battery through the connector cradle to the hand-held unit. The cart-based unit still further comprises a cart-based unit controller adapted to control the cart-based unit RF transceiver, the cart-based unit display, and communications between the cart-based unit and the hand-held unit via the connector cradle. According to this embodiment, the cart-based unit is adapted to receive the hand-held unit location information via the connector cradle, the hand-held unit is adapted to electrically interconnect the hand-held unit to the cart-based unit via the connector cradle for providing the hand-held unit location information to the cart-based unit, and the base station controller is adapted to manage communication between the central base station unit and the cart-based unit.
According to one embodiment of the invention that uses differential GPS technology, the base station unit further comprises a base station GPS receiver and a base station processor adapted to generate a GPS correction signal that is a function of the difference between a known base station location and the GPS-derived base station location. In this system, the cart-based unit is preferably adapted to receive the GPS correction signal transmitted from the base station unit via the cart-based unit RF transceiver and to provide the GPS correction signal to the hand-held unit via the connector cradle. The hand-held unit preferably generates hand-held unit location information from a combination of the GPS-derived hand-held unit location data and the GPS correction signal.
According to another embodiment of the invention that uses WAAS satellite correction signals to compensate for GPS system inaccuracies, the base station unit further comprises a base station WAAS receiver adapted to receive a WAAS correction signal and a base station processor adapted to determine WAAS correction data from the WAAS correction signal. In this system, the cart-based unit is preferably adapted to receive the WAAS correction data from the base station unit via the cart-based unit RF transceiver and to provide the WAAS correction data to the hand-held unit via the connector cradle. The hand-held unit preferably generates hand-held unit location information from a combination of the GPS-derived hand-held unit location data and the WAAS correction data. In still another embodiment that uses WAAS satellite correction signals, the hand-held unit GPS receiver is adapted to receive WAAS correction signals and the hand-held unit is adapted to generate hand-held unit location information from a combination of the GPS-derived hand-held unit location data and the WAAS correction data.
According to another advantageous embodiment, the invention provides a hand-held distant determining unit for use in a system based on differential GPS technology for determining distances to a plurality of user selected points of interest on a golf course. In this embodiment, the hand-held distance determining unit includes a hand-held unit GPS receiver adapted to receive and process navigation signals from GPS satellites and to thereby provide GPS-derived hand-held unit location data, a hand-held unit display for displaying graphics, distance information, location information, and other information to a user of the system, a hand-held unit memory for storing a plurality of stored location data for the respective ones of the points of interest on the golf course, and a hand-held unit controller adapted to control the hand-held unit GPS receiver, the hand-held unit display, and the hand-held unit memory. According to this embodiment, the hand-held unit controller is adapted to generate hand-held distance determining unit location information from a combination of the GPS-derived hand-held unit location data and the GPS correction signal. The hand-held unit is adapted to calculate a distance between the hand-held distance determining unit and a selected one of the points of interest on the golf course by comparing the hand-held distance determining unit location information with the stored location data for that respective point of interest, and the hand-held distance determining unit is further adapted to electrically interconnect the hand-held distance determining unit to the cart-based unit via the connector cradle for providing the hand-held distance determining unit location information to the cart-based unit and for receiving the GPS correction signal from the cart-based unit. In one advantageous embodiment, the hand-held unit is adapted to receive a paging message and other information from the central base station through a hand-held unit RF transceiver.
According to yet another advantageous embodiment, the invention provides a hand-held distance determining unit for use in a system based on WAAS correction signal technology for determining distances to a plurality of user selected points of interest on a golf course. In this embodiment, the hand-held distance determining unit includes a hand-held unit GPS receiver adapted to receive and process navigation signals from GPS satellites and to thereby provide GPS-derived hand-held unit location data, a hand-held unit display for displaying graphics, distance information, location information, and other information to a user of the system, a hand-held unit memory for storing a plurality of stored location data for the respective ones of the points of interest on the golf course, and a hand-held unit controller adapted to control the hand-held unit GPS receiver, the hand-held unit display, and the hand-held unit memory. According to this embodiment, the hand-held unit controller is adapted to generate hand-held distance determining unit location information from a combination of the GPS-derived hand-held unit location data and WAAS correction data. The hand-held unit is adapted to calculate a distance between the hand-held distance determining unit and a selected one of the points of interest on the golf course by comparing the hand-held distance determining unit location information with the stored location data for that respective point of interest, and the hand-held distance determining unit is further adapted to electrically interconnect the hand-held distance determining unit to the cart-based unit via the connector cradle for providing the hand-held distance determining unit location information to the cart-based unit and for receiving the GPS correction signal from the cart-based unit. In one advantageous embodiment, the hand-held unit is adapted to electrically interconnect the hand-held distance determining unit to the cart-based unit via the connector cradle for receiving information from the cart-based unit, the cart-based unit being adapted to receive the information from the central base station unit via the cart-based unit RF transceiver and to provide the information to the hand-held unit via the connector cradle.
According to another advantageous embodiment, a hand-held distance determining unit for use in a system for determining distances to a plurality of user selected points of interest on a golf course is provided. According to this embodiment, the hand-held distance determining unit includes a hand-held unit GPS receiver adapted to receive and process navigation signals from GPS satellites and to thereby provide GPS-derived hand-held unit location data, the hand-held unit GPS receiver being further adapted to receive and process a WAAS correction signal and to generate a WAAS correction data, a hand-held unit display for displaying graphics, distance information, location information, and other information to a user of the system, a hand-held unit memory for storing a plurality of stored location data for the respective ones of the points of interest on the golf course, and a hand-held unit controller adapted to control the hand-held unit GPS receiver, the hand-held unit display, and the hand-held unit memory. According to the invention, the hand-held unit controller is adapted to generate hand-held distance determining unit location information from a combination of the GPS-derived hand-held unit location data and the WAAS correction data, and the hand-held unit is adapted to calculate a distance between the hand-held distance determining unit and a selected one of the points of interest on the golf course by comparing the hand-held distance determining unit location information with the stored location data for that respective point of interest.
A method of determining distances to a plurality of selected points of interest on a golf course using GPS satellite position signals is also provided that is based on differential GPS techniques. According to this embodiment, the method includes the steps of determining an absolute location of a central base station relative to a fixed coordinate system, receiving at the base station a first set of navigation signals from the GPS satellites, determining a GPS-derived base station location relative to the fixed coordinate system from the first set of navigation signals, calculating a GPS correction signal that is a function of the difference between the absolute location of the central base station and the GPS-derived base station location, transmitting the GPS correction signal to a cart-based unit, inserting in the cart-based unit a hand-held unit having a hand-held unit display into a connector cradle that provides an electrical interconnection between the cart-based unit and the hand-held unit, relaying the GPS correction signal from the cart-based unit to the hand-held unit, storing a plurality of stored location data associated with the selected points of interest on the golf course, receiving in the hand-held unit a second set of navigation signals from the GPS satellites, determining a GPS-derived hand-held unit location relative to the fixed coordinate system from the second set of navigation signals, calculating a corrected hand-held unit location relative to the fixed coordinate system from a combination of the GPS-derived hand-held unit location and the GPS correction signal, determining a distance data between the hand-held unit and a first point of interest on the golf course by comparing the corrected hand-held unit location with the stored location data associated with the first point of interest, and displaying the distance data. on the hand-held unit display In one embodiment, the method further includes the steps of relaying the distance data from the hand-held unit to the cart-based unit through the connector cradle and displaying the distance data on a cart-based unit display.
A method of determining distances to a plurality of selected points of interest on a golf course using GPS satellite position signals is also provided that is based on transmitting WAAS correction signals from a central base station. According to this embodiment, the method includes the. steps of receiving at a central base station a WAAS correction signal from a WAAS broadcaster, calculating a WAAS correction data from the WAAS correction signal transmitting the WAAS correction data to a cart-based unit, inserting a hand-held unit having a hand-held unit display into a connector cradle in the cart-based unit that provides an electrical interconnection between the cart-based unit and the hand-held unit, relaying the WAAS correction data from the cart-based unit to the hand-held unit, storing a plurality of stored location data associated with the selected points of interest on the golf course, receiving in the hand-held unit a set of navigation signals from the GPS satellites, determining a GPS-derived hand-held unit location relative to a fixed coordinate system from the set of navigation signals, Calculating a corrected hand-held unit location relative to the fixed coordinate system from a combination of the GPS-derived hand-held unit location and the WAAS correction data, determining a distance data between the hand-held unit and a first point of interest on the golf course by comparing the corrected hand-held unit location with the stored location data associated with the first point of interest, and displaying the distance data on the hand-held unit display.
A method of determining distances to a plurality of selected points of interest on a golf course using GPS satellite position signals is also provided that is based on receiving WAAS satellite correction signals directly at a hand-held unit. According to this embodiment, the method includes the steps of receiving a WAAS correction signal from a WAAS broadcaster, calculating a WAAS correction data from the WAAS correction signal, storing a plurality of stored location data associated with the selected points of interest on the golf course, receiving a set of navigation signals from the GPS satellites, determining a GPS-derived hand-held unit location relative to a fixed coordinate system from the set of navigation signals, calculating a corrected hand-held unit location relative to the fixed coordinate system from a combination of the GPS-derived hand-held unit location and the WAAS correction data, determining a distance data between the hand-held unit and a first point of interest on the golf course by comparing the corrected hand-held unit location with the stored location data associated with the first point of interest, and displaying the distance data on the hand-held unit display.
The system and method of the present invention thus advantageously combine the benefits of a cart-mounted GPS-based system and method for distance determination with the benefits of a portable, small, low power, low cost GPS-based hand-held unit. The hybrid system features a hand-held unit that can be interconnected with a cart-based unit when it is inserted into a connector cradle in the cart-based unit, and the two units can thereby exchange GPS correction signals, WAAS correction data, location and distance information, paging information, and/or other information. The performance and cost trade-offs by which conventional systems for GPS-based golf course position determination are typically constrained are thus avoided.